This invention relates to a curable composition and especially to those that can have controlled cure through the use of appropriate curing agents. In its most preferred and presently useful form the invention provides relief printing plates which are characterized by unusually rapid photochemical cure rates, improved solvent resistance and non-tacky surfaces while retaining the many desirable properties espoused for other plates and often with enhanced quality.
Many patents independently reveal various features of the inventive composition. They however lack the overall advantage presented by the synegistic activity of the present new composition. British Pat. No. 1,395,822 discloses a composition having an A-B-A type block copolymer present in an amount of at least 40% by weight, at least 5% by weight of an addition photopolymerizable polyethylenically unsaturated acrylic or methacrylic acid ester containing two or more acrylate or methacrylate groups per molecule and 0.1 to 10% by weight of an addition polymerizable initiator activatable by actinic light. As a preferred embodiment the British Pat. No. 1,395,822, discloses a composition having 60-85 parts by weight of the block copolymer, 40-75 parts by weight of ethylene glycol diacrylate or methacrylate, trimethylolpropane triacrylate or methacrylate or pentaerythritol tetraacrylate or methacrylate and from 1.5 to 4.0 parts by weight of benzophenone. An optional identified ingredient is liquid rubber polymer having a molecular weight between 750 and 3000, in a preferred embodiment 5-30 parts by weight of liquid polybutadiene.
Another patent showing an A-B-A block copolymer composition is U.S. Pat. No. 3,674,486. This is represented by control Example XIII of the present application. Yet another A-B-A block copolymer composition is disclosed in British 1,366,769. A-B block copolymer compositions are disclosed in German Patent Publications DT OS No. 24 56 439 and DT OS No. 26 10 206.
As is illustrated in Table 1 of the present application the compositions of the above references are less rapid in curing than the compositions of the present invention. This is also illustrated by Example I-VI as contrasted with Control Examples VII-XII which also illustrate that the composition of the present invention produces printing plates that are not tacky while printing plates produced from the composition of the above references are tacky.
There are a number of U.S. and foreign patents that show photocurable compositions that have as a major chemically functioning constituent a polythiol. This is unlike the present invention where the polythiol constituent seemingly acts in some way to regulate and make more effective the polymerization of the other constituent components of the composition. The curable compositions of the present invention, as a general rule cure within minutes without the presence of the polythiol. Examples of patents that show photocurable compositions that have a polythiol as a major chemically functioning constituent are U.S. Pat. Nos. 4,008,341; 3,843,572; 3,832,421; 3,783,152; 3,666,461; 3,661,744; 3,627,529 and 3,615,450 and Canadian Pat. Nos. 930,094; 926,183; 924,047 and 885,388.